I want to share my experience of using Pixracer as a RACER.
That is my first experience of using Pixracer board and this experience was not great at all (compared to Pixhawk and Naze32)
- The first thing is that bundled ESP8266 WiFi never worked for me. (I was able to connect to wifi hotspot, but QGC never detected the board).
- Pixracer board and ACSP4 don't seems to be designed for racers
- These 2 boards can't be aligned the way to use short power cable and still fit into spacious ZMR250 frame
- Pixracer board has 2 telemetry ports, CAN and GPS connectors. This all takes extra space and weight which is critical for the racer and will not be used in 99.9% cases.
- There are a lot of connectors on the outer sides of the board and they are the first that will be teared off from it. The first one for be was debug port, second - FrSky telemetry port.
- All the stock settings for frames are
stabilized mode oriented and have very low
I rate gains. The most critical here is
I gain, in my case it end up slightly higher
P gain. I have spent a lot of time trying to figure out how to tune it right. I was trying to follow the tuning manual from the px4.io, but it is totally not-relevant for tuning racer (ACRO mode in general). This article helped me greatly on tuning http://myfirstdrone.com/tutorials/how-to-tune-a-quadcopter/
- PID tuning with QGC is a pain, especially if you have to use USB connection:
- The biggest issue is that there is no PID tuning screen, you have to look them up in the general parameters table. So I have developed a PID screen for QGC (will post PR some time soon)
- If you connect USB while board is powered via the battery QGC will fail to recognize board in 99% of the cases and you will have to restart it. So EVERY single time you need to adjust PID you have to unplug battery and connect USB wait for board to boot, change settings, connect battery back and wait again. This takes enormous amount of time. With Naze32/Cleanflight you can connect USB and GC recognizes it and shows last screen in 1 second or less. It makes tuning very enjoyable. To workaround this I am trying to get BT connection to the board working.
- Another issue with PX4 stack in general for ACRO flight is that there is no Expo mode in the flight controller itself and no "Super-expo" or its analogy. It is critical as racers use Expo of 65-85 and having such a big expo on the Tx side significantly reduces sticks resolution. More details on this can be found here https://oscarliang.com/rc-roll-pitch-yaw-rate-cleanflight/
- Low throttle flight (20-40%) is very unstable with PX4. It starts to fall to one of the sides or back/front. It might be because of lack of
I gain at this throttle. So I am going to play with TPA and gains.
Conclusion - Pixracer and PX4 are not RACER ready but definitely heading this way. If I manage get a replacement boards I might continue contributing to this stack and will implement Expo and Super-expo for the px4, if not I will switch to Cleanflight.